1. Field of the Invention
The present invention generally relates to fire barriers for use in voids formed in buildings, and more particularly, pertains to systems that continue to maintain an effective barrier against the spread of fire despite a substantial relative displacement or distortion of the surfaces that define such voids.
2. Description of Related Art
A variety of dynamic voids or joints are typically incorporated in a building in order to prevent damage as the structure undergoes movement due to thermal, wind and seismic loads. In order to prevent the spread of heat, smoke, and flames therethrough, such voids must be fitted with fire barriers. It is especially important for a fire barrier fitted to a joint to remain in tact after the joint has undergone substantial displacement or distortion due to seismic activity, as the risk of fire is especially high immediately following an earthquake.
Various barrier systems have been devised that attempt to accommodate the magnitude of movement anticipated during a seismic event. A substantial widening and/or narrowing of a seismic joint can be expected, while lateral or shear displacement on the order of several feet is not unusual. Fire barriers typically consist of a sheet of flexible material that is attached to each wall of the joint and loosely draped therebetween. Such configuration does not in any way impede the narrowing of the gap while the slack in the material accommodates a widening of the gap beyond its nominal width. Any differential vertical displacement between the two sides of the joint, is similarly compensated for by the flexible material. In order to prevent failure of such a barrier when the joint undergoes substantial lateral displacement, various mechanisms have additionally been provided in order to allow one or both sides of the barrier to shift along the walls of the joint. Some configurations provide for the barrier to be rigidly affixed to one side of the joint while the opposite edge of the barrier is slideably retained in a groove or track attached to the opposite wall of the joint. Alternatively, both edges of the barrier are retained within grooves or tracks formed in both sides of the joint in order to allow both sides to shift laterally relative the walls of the joint.
These prior art fire barriers suffer from a number of shortcomings. First and foremost, as the joint walls shift laterally in the described systems, substantial shear loads are transferred to the barrier material due to the friction inherent in the groove or track attachment configurations. Any distortion, damage or obstruction of the retaining tracks further aggravates the potential for failure. Furthermore, such systems are relatively complex and their retrofitment to typical in-place joint configurations may be problematic and therefore very costly.